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Re: Space Shuttle - Flight

Postby Hooray » Mon Mar 15, 2021 9:41 pm

Thorsten wrote in Mon Feb 15, 2021 1:40 pm:
Can't we make use of OOP magic to run two JSBsim instances in different threads, one for the shuttle and the other for the orbital target?

Who is 'we'? I can't make that, so the question is, can you? :mrgreen:



FWIW, at some point, FlightGear did have support for an external FDM mechanism that would allow JSBSim PROCESSES to drive FlightGear, and people were also using multiple instances to do so.
Aside from that, there have been talks on the jsbsim mailing list about using some sort of embedded FDM/sub-FDMs (simulation in the loop) - some of that was discussed in the context of calculating VNAV profiles by running the FDM in "look-ahead" mode.

Speaking in general, with modern CPUs there's no need for threading here - even back in the early 2000s David Megginson actually suggested to support multiple /fdm entries in the main property tree, in the form of fdm[0] ... fdm[x] entries, which would get their own custom time-slices/update rates. by multi-plexing between different /position, /orientation nodes for each aircraft.

At the time, the rationale was that coding/using and maintaining pseudo FDMs for AI traffic would quickly become more complicated than running a "real" FDM with reduced fidelity (lower simulation rate/resolution).

At the time, FlightGear internally used the so called "FDMShell" mechanism to abstract away the differences between different FDMs - but that mechanism should still work today, and should not require any threading, but it would certainly require C++ changes. Back in the early days of the project, the "external FDM" mechanism was the only way to get the FDM off onto its own core (because it would run in a dedicated process)

For details about the parent/child FDM functionality, see Jon's comments quoted here: https://wiki.flightgear.org/Implementin ... Child_FDMs

Again, it might be best to check back with the JSBSim folks for details - either way, I doubt that this would involve any significant OOP or threading.
I cannot currently find David's proposal about multiple /fdm nodes in the main property tree, but he discussed the idea with Jon - and the context was indeed AI traffic driven by actual JSBSim instances, rather than using the pseudo FDM approach we're today still using.

More recently, Erik implemented DDS support and also provided FDM integration - besides, he's been around long enough, so he might remember a few more details, given that he's also been involved in JSBSim. But running multiple instances of JSBSim should not be such an issue, other projects have been doing that for years unless I am missing something ?

EDIT: Here's some of the context surrounding FDM driven AI traffic using FDM multiplexing or multiple FDM instances: https://wiki.flightgear.org/An_Integrat ... AI_Traffic
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Re: Space Shuttle - Flight

Postby wkitty42 » Tue Mar 16, 2021 1:24 pm

Hooray wrote in Mon Mar 15, 2021 9:41 pm:More recently, Erik implemented DDS support and also provided FDM integration

to be clear, this is Data Distribution Service (using CycloneDDS)... it is not related to the DDS (Direct Draw Surface?) texture cache...
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Re: Space Shuttle - Flight

Postby GinGin » Tue Mar 16, 2021 2:51 pm

@Hooray: Very interesting reading, I will save that.
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Re: Space Shuttle - Flight

Postby GinGin » Tue Mar 16, 2021 11:30 pm

Another interesting scenario with a severe underspeed at MECO (700 fps).
Huge OMS 1 required to raise our perigee and then either go for an AOA or a sub nominal Orbit.

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Re: Space Shuttle - Flight

Postby GinGin » Wed Mar 17, 2021 4:39 pm

Working on a TAL video with multiple failures following that STS 135 TAL sim session:

https://www.youtube.com/watch?v=XTJ2pCK5Apw

The good thing is: we can simulate a lot of failures in those list.
I will go with Main C failure, then GPC 2 failure, Cabin Leak and 3 engines TAL to Istres, and finally APU 1 failure during last part of entry

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One GPC failure during the ascent, quite interesting and a small event. No reconfiguraiton while in dynamic flight ( pre MECO)
Post MECO and before transitionning towards OPS3, we need to reassign the Buses that were linked to GPC 2 ( One string and one crt bus to recover crt screen drivent by IDP 2).
Then GPC is halted, as we can see in the picture below ( nothing in the GPC 2 column)

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Then let's go for the entry

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And a No Yaw Jet test during the major part of it, watching the Shuttle going high and low on drag due to sluggisher reaction (we can see it with the Box Guidance that moves quite a lot) , but staying around the Nominal center line 8)

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Welcome to Istres

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Re: Space Shuttle - Flight

Postby GinGin » Wed Mar 24, 2021 12:55 pm

Back to Hawai after a tough Entry with high Orbital enrgy

Almost at TAEM interface

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90° into the HAC

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Some spotters are there to welcome the big glider

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Re: Space Shuttle - Flight

Postby GinGin » Sun Mar 28, 2021 9:49 pm

Aurora Glory during Entry

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Alaska sightseeing Tour

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Re: Space Shuttle - Flight

Postby GinGin » Wed Apr 14, 2021 4:50 pm

STS 1 look-alike

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Re: Space Shuttle - Flight

Postby GinGin » Mon May 03, 2021 4:06 pm

Some good fun with Auto Roll/Yaw for Landing in marginal weather conditions.
Cross-Wind up to 15 kts and ceiling between 100 and 300 feet.
RVR up to 1000 m



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Re: Space Shuttle - Flight

Postby Johan G » Mon May 03, 2021 6:23 pm

Why do I get Halloween vibes from the last two screenshots? :lol:
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Re: Space Shuttle - Flight

Postby GinGin » Fri May 07, 2021 6:00 pm

I get Halloween vibes


Let's move to Summer end of the day Cb's vibe :)

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Re: Space Shuttle - Flight

Postby GinGin » Sat May 08, 2021 10:45 pm

Still in the Middle of TAEM testing with marginal weather.

Here at Istres with some Showers of Rainc in short final

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A more worrisome situation in Florida with heavy sea breeze

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And a hard landing on the right wheel :mrgreen:

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Re: Space Shuttle - Flight

Postby GinGin » Thu May 27, 2021 9:27 am

Some more tests about the TAEM pitch loop, based on a radial acceleration commanded now.
AP fully available until Pre-Flare (2000 feet) for now.


IFR approach in Easter Island

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Breaking the heavy clouds layer at 4000 feet, AP is smooth and on trajectory

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Manually flown final flare after the cliff

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Re: Space Shuttle - Flight

Postby wlbragg » Thu May 27, 2021 10:32 pm

. Nice, I want to give this one a try!
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Re: Space Shuttle - Flight

Postby Thorsten » Fri May 28, 2021 6:14 am

This looks seriously scary weather - better have the state vector in perfect order!
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